The advancing electrolytic capacitor industry has, at its premium level, increasing capacitances per units of volume and weight of the sintered powder porous compacts anodes (usually refractory metal powders, preferrably tantalum powder) that constitute the anode of the capacitor. This performance enhancement is characterized by fine powder sizes, miniaturization of the compact as a whole and selected additives to the tantalum powders to enhance capacitor performance and/or the manufacturing process regarding one or more of capacitance, sinterability and resistance to electrical leakage and voltage breakdown. Known additives for one or more of such purposes include phosphorous, silicon, nitrogen and other elements.
Improvements in electrical leakage have been made through improvements of anode compacts per se. The present invention has as a principal object enhancement of leakage characteristic (reduction) through modification of lead wire chemistry.
The present invention provides a method of enhancing (lowering) leakage of capacitors by modifying the lead wire surface by doping with one or more interstitial elements such as nitrogen, oxygen or silicon.
The doping can be practiced by placing a finished wire into a gaseous atmosphere containing a sufficiently high concentration of the interstitial element(s) and heating for driving the element(s) into the wire surface. The interstitial element(s) can also be introduced into the bulk of the wire (at wire stage or at an earlier stage of fabrication) and then segregated to near the surface. It has been discovered that capacitor leakage can be reduced using such modified lead wires.
The interstitial element(s), if provided in too high a concentration throughout the wire bulk can have a deleterious effect. But surface doping can achieve leakage enhancement without adverse mechanical effect.
The lead wire is bonded to a sintered powder porous anode of the type used for electrolytic capacitors.